1. Field of the Invention
The present invention relates to a vertical handover between a cellular network and Internet Protocol (IP) network. More particularly, the present invention relates to an inter-network packet transmission method and system for vertical handover between a cellular network and Internet Protocol (IP) network.
2. Description of the Related Art
When a dual mode User Equipment (UE) having a cellular communication interface and a Wireless Local Area Network (WLAN) interface attempts a vertical handover from a WLAN to a cellular network, the UE releases the IP address assigned from the WLAN and receives a new one from the cellular network. Here, vertical handover is a technique that allows a UE to roam between heterogeneous networks operating with different access technologies.
In a WLAN, an IP packet is delivered to a destination UE via an Access Point (AP) connected to an Access Router (AR). The AR is responsible for routing IP packets in the IP network and for vertical handover to and from the cellular network. The AP provides a network access service and acts as a bridge between the WLAN and wired network.
Recently, research has been done to develop a dual mode mobile terminal that supports voice and data call handovers between the cellular network and WLAN. Accordingly, an improved inter-system handover technique is required. A standard for inter-system voice call handover, using a Voice Call Continuity technique, has almost been finalized, and a standard for the inter-system data call handover technique is in the middle of being completed.
The 3rd Generation Partnership Project (3GPP) specifies a Gi interface between a Gateway General Packet Radio Service (GPRS) Support Node (GGSN), which is an element of a cellular network, and a Packet Data Network (PDN), and a Wi interface between a Packet Data Gateway and a PDN. In order to hand over a data call between the circuit switched cellular network and the packet switched WLAN, it is required to modify a routing table to a Root Router to which the route to a destination terminal is connected or required to establish a new route between the two terminals using a Stream Control Transmission Protocol (SCTP).
In the case of the route modification technique, however, since the route to the root router is non-determinative, it is difficult to apply the conventional route modification-based handover to a delay sensitive real time packet transmission service. Also, the conventional SCTP-based handover technique is limited in universal application since both the terminals involved in a communication should support the SCTP.